ILLUSTRATIONS 



FIGURE PAGE 



tilaginous braincase and primary upper jaw of foetal 

 salamander. (After Gaupp.) 



C. Skull of primitive fossil reptile (Diadectes) from 

 the Permo- Carboniferous of Texas. 



In C the bony mask covering the temporal region is cut 

 through and a part of it removed to show the primary 

 upper jaw (comprising the palatine, pterygoid, epi- 

 pterygoid and quadrate bones) and their relations to the 

 braincase. 



63. — Under Side of the Skull of (A) Devonian 

 Fossil Fish (Lobe-finned), Air-breathing 

 Crossopt (Eusthenopteron) and (B) Primi- 

 tive Fossil Amphibian (Baphetes) . (A after 

 Bryant and Watson; B after Watson) . 108 



The secondary upper jaws (premaxillse, maxillae) 

 are on the margins; the primary upper jaws (palato- 

 quadrates) are largely covered by tooth-bearing plates 

 of the primary palate. 



64. — Right Half of the Lower Jaw of Lobe- 

 finned Fossil Fish (A, C), and Primitive 

 Fossil Amphibian (B, D), and Recent 

 Turtle Embryo (E) . . .111 



A. Megalichthys, outer side. (After Watson.) 



B. Trimerorhackis, outer side. (After Williston.) 



C. Megalichthys, inner side. (After Watson.) 



D. T rimer orhachis, inner side. (After Williston.) 



E. Recent turtle embryo, inner side. (After 

 Parker.) 



Abbreviations of names of bones: ang, angular; art, 

 articular; cor, coronoids (I, II); dn, dentary; preart, 

 prearticular; pospl, postsplenial; spl, splenial; surang, 

 surangular bone. 



In the embryo turtle Meckel's cartilage is very 

 plainly seen on the inner side of the jaw, extending the 

 full length of the jaw. The rear end forms the articu- 

 lar bone of the adult. 



These jaws are made mostly of the dermal sheathing 

 bones that in the embryo surround the primary carti- 



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